Method of laser coagulation of blood vessels

ABSTRACT

The subject invention relates to laser medicine, in particular to dermatology and can be used for medical treatment of hemangioma, treatment and prophylaxis of phlebectasia and other vascular lesions. The invention solves the problem of increasing the effectiveness of blood vessels coagulation while diminishing the probability of causing traumatosis of surrounding soft tissue.  
     The method comprises the steps of subjecting the blood vessel to the influence of pulse ra-diation with wavelength of 500-600 nm, energy density up to 10 Joules/cm 2  during not more than 10 ms and simultaneously subjecting the same vessel to the influence of additional radiation with at least one more wavelength in the range of 800-1400 nm and energy density not exceeding 100 Joules/cm 2 . The energy density and influence duration are chosen depending upon the size of the vessel to be coagulated. The radiation may be applied either by single pulses with a duration of not more than 10 ms, or by a packet of several nanosecond pulses the duration of which does not exceed 10 ms.

TECHNICAL FIELD

The subject invention relates to laser medicine, in particular to dermatology, and can be used for medical treatment of hemangioma, treatment and prophylaxis of phlebectasia and other vascular lesions.

BACKGROUND ART

A method of laser coagulation of vessels by argon laser, radiation wavelength 488-514 nm is known [“Laser surg. Med.”, 1992, vol.12, pp. 246-253. “Applied laser medicine”. Edited by H. P. Berlien, G. Y. Muller, pp. 326-327, 1997].

The medical effect in this case is based on the fact that argon laser radiation is absorbed well enough by hemoglobin as a result of which the temperature inside the vessel is being raised and the coagulation of the latter takes place.

But the radiation with such wavelength is not able to penetrate deep into blood vessels, hence the method cannot be used for the coagulation of big vessels. Moreover, the argon la-ser radiation is also well absorbed by other skin constituents what, on one hand, leads to the overheating of surrounding tissue and, on the other hand, diminishes the medical effect even in coagulation of small vessels.

A method of vessels coagulation with YAG:Nd laser operating in the mode of the second harmonic generation is also known in the art [U.S. Pat. No. 5558667, publication date 24 Sep. 1996, “Method and apparatus for treating vascular lesions”].

The said laser radiation with the wavelength of 532 nm, pulse duration of 0.5-10.0 ms and energy density of 10-20 Joules/cm² is also well absorbed by hemoglobin what allows to coagulate small blood vessels. The disadvantage of the said method lies in the fact that beside hemoglobin other constituents of soft tissue also absorb the said radiation and the skin penetration deepness is not sufficient which does not allow to coagulate the vessels without causing damage of the surrounding soft tissue.

The most close to the present application art is a method of vessels coagulation with the dye laser radiation by pulses with the wavelength of 585 nm [Treatment of Vascular Lesions in Pigmented Skin with the Pulsed Dye Laser, “Laser surg. Med.”, 1992, suppl. 4, pp.65-74].

Such wavelength allows deeper penetration into soft tissue at the expense of lesser absorption by various skin constituents. The absorption effectiveness of the said radiation by hemoglobin is less than that of the argon and the second harmonic YAG:Nd lasers, though it is compensated that the radiation penetrates deeper inside the vessel causing blood coagulation in greater volumes. Owing to this fact the said method allows to coagulate big vessels. However, to heat effectively the whole vessel volume it is necessary to use greater energies as with smaller energies a partial blood coagulation may occur which will not provide sufficient vessel walls heating and may cause displacement of the coagulated blood portion during blood circulation. Besides, the use of big energies radiation in the given wavelength range provokes substantial overheating of the surrounding tissue, what may result in irreversible changes in them.

DISCLOSURE OF INVENTION

The object of the invention is to solve the problem of increasing the effectiveness of blood vessels coagulation while diminishing the probability of causing traumatosis of the surrounding soft tissue.

The assigned problem is solved by pulse radiation influence of the blood vessels with wavelength of 500-600 nm, energy density up to 10 Joules/cm² during not more than 10 ms. Simultaneously the same vessel is influenced by at least one more additional radiation with wavelength in the range of 800-1400 nm and energy density up to 100 Joules/cm².

The energy density and the influence duration are chosen depending upon the size of the vessel to be coagulated. The radiation may be applied either by single pulses during not more than 10 ms, or by a packet of several nanosecond pulses the duration of which does not exceed 10 ms.

The subject method is based on simultaneous influence of radiations with different wavelengths each of which separately cannot result in effective vessel coagulation. For all that the radiation is applied either by way of a single pulse with a duration from hundreds of microseconds to tens of milliseconds, or by way of a pulse packet of nanosecond duration, in such case the packet duration should not exceed 10 milliseconds. The additional radiation wavelength range is chosen taking into account the condition of the poor absorption of skin constituents, i.e. deep penetration of the radiation into soft tissue.

The comparison of the proposed method with its prototype allows to reveal the following distinguishing features:

-   -   at least one more additional radiation with another wavelength         is used for the blood vessel coagulation;     -   both radiations influence the vessel to be coagulated         simultaneously;     -   the additinal radiation wavelength is chosen taking into account         the condition of its deep penetration into the skin soft tissue;     -   for the coagulation of the blood vessel are used either single         pulses, or a packet of nanosecond pulses with corresponding         duration and energy density.

All the aforesaid allows to make a conclusion as to the conformity of the subject solution to the criterion “New in the Art”.

Despite the fact that methods of laser coagulation of blood vessels are known in science and medical practice the claimed for method allows to obtain a new result. The effect of the spectrum absorption variation of the vessel being coagulated is not taken into consideration in the known methods. In the claimed for method the coagulation process is effected by at least two simultaneous radiations with different wavelengths, the first of which creates inside the vessel separate zones of coagulated blood which are the absorption centres for the radiation with the second wavelength which, in its turn, effects heating of the said centres accompanied by subsequent coagulation of the whole blood vessel.

The first radiation with the wavelength in the range from 500 to 600 nm is effectively absorbed by hemoglobin and under the influence of this radiation the coagulation of blood portions takes place and as this radiation cannot penetrate deep into blood vessels, so the coagulation centres are situated in the zone directly bordering the vessel's walls which contributes to their effective heating and coagulation. Under the influence of the additional radiation the temperature of the coagulated blood portions increases and the heat is transmitted to the non-coagulated blood portions causing their heating and the vessel's coagulation.

Moreover, the absorption spectrum of coagulated blood allows to use the additional radiation in the wavelength range from 800 to 1400 nm which is little absorbed by the skin and noncoagulated vessel's zones and due to this fact reduces the heating of surrounding soft tissue.

The influence on the vessel to be coagulated by simultaneous radiations with different wavelengths allows to raise the coagulation effectiveness and reduce the traumatosis of surrounding tissue.

As the wavelength of the first radiation is effectively absorbed by the skin and at prolonged influence may cause the undesirable overheating, so the time of the first radiation influence may be chosen as minimum, or its intensity may be decreased towards the end of influence time. The radiation with the second wavelength in its turn is formed with inverse relationship, i.e. its intensity may be increased towards the end of influence period. By controlling the pulses duration and the radiation intensity it is possible to effect selective regulation of temperature in a big blood vessel at minimum thermal heating of surrounding soft tissue.

All the aforesaid allows to come to the conclusion as to the conformity of the claimed solution to the criterion “Inventive Level”.

INDUSTRIAL APPLICABILITY

The biologic tissue is being influenced by a laser radiation either by way of two compatible in time pulses, or by way of two packets of nanosecond pulses. To generate radiation with wavelengths in the ranges of 500-600 nm and 800-1400 nm it is possible to use YAG:Nd laser with the active modulation of the Q-factor and generation of the second harmonic. In this case the radiation intensity of the second harmonic will be in non-linear dependence on the intensity of the first one.

Under the radiation influence with the wavelength of 532 nm, energy density of 10 Joules/cm² with duration of 5 ms and spot diameter of 1 mm in the biological tissue—blood vessel a partial coagulation takes place and zones of coagulated blood are formed. Simultaneously the same vessel is being influenced by radiation with the wavelength of 1064 nm at energy density of 70 Joules/cm² during 10 ms and spot diameter of 1 mm. This radiation influences the coagulated zones in the vessel and effects complete vessel coagulation not causing damage to surrounding soft tissue. 

1. A method of laser coagulation of blood vessels by way of subjecting the vessel to the influence of pulse radiation with wavelength of 500-600 nm, energy density of not more than 10 Joules/cm² with duration for not more than 10 ms, characterized by that the same vessel is simultaneously subjected to additional radiation with at least one more wavelength in the range of 800-1400 nm and energy density of not more than 100 Joules/cm².
 2. The method as set forth in claim 1, characterized by that the energy density and influence duration are chosen depending upon the size of the vessel to be coagulated.
 3. The method as set forth in claims 2, characterized by that the radiation in applied in single pulses during not more than 10 ms.
 4. The method as set forth in claim 2, characterized by that the radiation is applied by way of a packet of several nanosecond pulses during not more than 10 ms. 